Dibromo-dicyanobutane such as 1,2-dibromo-2,4-dicyanobutane, 1,2-dibromo-1,4-dicyanobutane or 2,3-dibromo-1,4-dicyanobutane is useful as an intermediate for agricultural chemicals and pharmaceuticals. Particularly, 1,2-dibromo-2,4-dicyanobutane is industrially used as an antiseptic agent and mildewprooring agent which are effective against miscellaneous microorganisms which putrefy aqueous paints, adhesives, latices, emulsions, joint cements, woods and the like, and lower their viscosity.
The dibromo-dicyanobutane is produced by brominating an olefinic cyano compound. For example, 1,2-dibromo-2,4-dicyanobutane is produced according to the process disclosed in U.S. Pat. Nos. 3,877,922, 3,873,597, 3,833,731 and 3,644,380. The representative process is as follows.
2-Methyleneglutaronitrile is reacted in an aqueous medium with bromine which is added dropwise. After completion of the reaction, excess bromine is decomposed and removed by adding sodium bisulfite or the like. The solid reaction product which separates out after cooling is washed with water repeatedly, and the solid product obtained by filtering is dried under a reduced pressure.
The product thus obtained is preferably used in the form of fine powders, which increases the drying effect. Therefore, the pulverization of the product is usually accomplished prior to drying bulk solids formed. However, in order to attempt the pulverization in the course of the solid formation, a process wherein after decomposing excess bromine, a surfactant is added to emulsify, followed by cooling, is proposed.
It has been found that when 1,2-dibromo-2,4-dicyanobutane fine powder which was sufficiently washed with water is dried using a drying apparatus made of SUS, the product after drying markedly colors in orange and has a very irritating odor. It has been also found that the colored product cakes and loses the fine powder form when stored in a container, a so-called "caking phenomenon" in the powder engineering. As a result, the SUS dryer used was corroded so severely that could not be further used.
The above problems deteriorate the quality of dibromo-dicyanobutane as the product in the various field of use thereof, resulting in remarkably decreasing the commercial value. The caking of the product requires to crush and pulverize the bulk product prior to withdrawing from a container or adding to a desired product, making the operation complicated. Further, the irritating odor is not preferred to operators from the hygienic standpoint.
To overcome those problems, the colored product was washed with water repeatedly, but the coloration did not disappear and the irritating odor did not lose. The problems may be overcome to some extent if the drying temperature is lowered and a dryer made of glass is used. Further, recrystallization using an organic solvent such as isopropanol may be of some help to overcome the problems.
However, the above proposals are difficult to sufficiently overcome the problems and are not industrially preferred manners in increasing a number of steps, cost for equipment, cost for workers and the like.